Fibrinogen (Fg) and fibrin (Fb) are proteolyzed by plasmin in physiological and pathological fibrinolysis. Plasma concentrations of Fg and/or Fb degradation products (FDP) are thus augmented. Therefore, a rapid and accurate determination of FDP would be clinically valuable. The problem will be approached by: (1) Development of double antibody radioimmunoassays (RIA) for FDP in plasma utilizing antibodies directed against the neoantigen of E and Y fragments, respectively, and (2) Establishment of solid-phase RIA for FDP in the plasma as a rapid and sensitive immunoassay method to determine the levels of blood FDP in patients, thus permitting quick and effective treatment of hemostatic dysfunctions. The neo-antigen RIA will be used to assay blood FDP in patients with consumption coagulopathy, and the data accrued will be related to the data from other laboratory clotting tests such as Fg concentration and thrombin time. The competitive inhibition profile of fibrinogen-E (Fg-E) versus fibrin-E (Fb-E) in our double-antibody RIA showed that one discriminating antiserum was capable of distinguishing between the two molecular species by differences in their displacement slopes. The linearization of standard curves by logit transformation has permitted the calculation of both Fg-E and Fb-E levels in plasma samples utilizing linear regression analysis. Therefore, we wish (3) To develop a RIA of hyper and hypocoagulable states which will distinguish a subtle structural variation between the FDP derived from Fg and Fb, leading to the distinction between a primary fibrinolytic state and a disseminated intravascular coagulation (DIC) followed by secondary fibrinolysis. Other methods of determining hypercoagulable states will be correlated with the data obtained from evaluation of FDP. Attempts will be made: (4) To use antithrombin III as a specific probe of DIC syndrome.